Devices for forming airlaid fibrous webs have been constructed to deposit fibrous material onto the foraminous surface of a moving forming belt having the configuration of an endless loop. For example, see U.S. Pat. No. 4,626,184 issued Dec. 2, 1986 to P. Hammond.
Devices for forming airlaid fibrous webs have also employed drumtype forming systems wherein the fibrous material is deposited onto a foraminous, outer peripheral surface of a revolving drum. For example, see U.S. Pat. No. 4,666,647 issued May 19, 1987, to K. Enloe et al. and entitled "Apparatus and Method for Forming a Laid Fibrous Web", and U.S. Pat. No. 4,761,258 issued Aug. 2, 1988, to K. Enloe and entitled "Controlled Formation of Light and Heavy Fluff Zones.
Conventional forming systems, such as those described above, have had various shortcomings. Forming drums have had relatively large diameters and can require excessive amounts of space. In addition, the forming drums have required complex sealing and baffling mechanisms to regulate the distribution of vacuum within the forming drum. Forming belt systems have had a limited ability to reliably produce desired contours in the thickness and basis weight of the formed fibrous web. The compactness of the forming belt system requires the forming belt to traverse around turn rolls having relatively small diameters. This requirement has limited the allowable thickness of the forming belt, and has limited the ability to incorporate a forming belt having significantly-sized depressions or other cavities formed into the belt surface. As a result, there has been a continued need for a belt-type of forming system that can more efficiently and more reliably produce a predetermined thickness and basis weight contour pattern onto the belt-side of the deposited, fibrous web.